I want some help for back pain during sitting meditation. Sometime I feel a sharp pain on my right spine tendon. I hope there is something I can do to ease it? Thank you.

Maybe try shorter meditations, instead of a very long one have two shorter ones a day.
You can sit on a chair for meditation, you might find it more comfortable. Try different positions, sitting on a chair, a sofa, lying down, putting your legs in a different position.
Don’t forget it’s all about being comfortable, do it your way.
Also maybe do some stretching exercises before meditation.
Hope you find your best position soon!

Do you sit on a cushion while meditating? If you don't, I suggest you do so. Or maybe make sure to use a comfy chair. In my experience as well, most meditation practices tell you to sit up straight, but if that gives you discomfort, I would think it would be better to slouch and keep up with your meditation routine than to sit straight and be tempted to quit.

It’s amazing you ask this! For I have a similar pain. To ease it I have to first; reconsider it as sensation (what is it), then; accept it for what it is. Then get really curious about what it is, how it changes and what happens when I allow my awareness to “melt” it.
Now this is when I am very present and clear, the key is gentle approach, if it’s too much, I lie down or adjust my position to allow me to explore it better.
For me mediation has become a lot more about trusting myself, trusting the body and letting the body lead the way toward my healing.

You can try do some light stretching the child pose would be good to start if it doesn't subside look for professional help

Fastest solution would be to lie down during meditation. My guess is the pain is *likely* caused by years of poor posture, because I deal with something similar. Look up how to sit with comfortable posture and practice it. It will come with time 🙏🏼